Field of the Invention
The invention relates to a method of controlling the level of printing ink in an ink fountain.
In printing machines, it has been known heretofore to top off the used printing ink in an ink fountain from a cartridge (published German Patent Document DE 196 36 985 D1). Because of the viscosity of the printing ink, the printing ink is discharged from the cartridge so that it is metered uniformly along an ink fountain roller that dips into the printing ink. The level of the printing ink in the ink fountain can be regulated by determining or registering the actual level continuously with the aid of a level sensor, by comparing the actual level with a desired or nominal level value and by deriving from the obtained comparative values, actuating signals for an actuating element of a pushing or expulsion device for the cartridge. The actuating signals effect the closest possible match between the actual state and the desired or nominal state.
It has also been known to register or determine the ink supply volume in the cartridge by suitable sensors and to generate a signal which indicates that the volume of ink supply is coming to an end. An operator of a printing machine that is operating continuously is thus given an opportunity to replace a used or depleted cartridge with a full cartridge. Any residue of printing ink in the used cartridge can be expelled beforehand into the ink fountain manually or by machine.
Heretofore known methods of topping off printing ink in an ink fountain have the disadvantage that, as a result of controlling the filling level to the most uniform level possible, the time which is available for changing a cartridge or a similar supply container is reduced. There is a risk that, in particular in the case of multicolor printing machines having a large number of printing units, changing a cartridge is not possible, because the operator is already busy with other operating procedures or cartridge changes. In such a case, the printing operation has to be interrupted and started up again, which reduces productivity. Topping off to a uniform level also has the disadvantage that, at the end of the print job, the respective level remains in the ink fountains. If a print job follows wherein printing is to be performed with other colors, the printing ink from the previous job has to be removed, a task that is complicated and gives rise to costs because, as a rule, these printing inks have to be removed inasmuch as they cannot be reused. A like disadvantage occurs when the printing machine is to be stopped, for example at the end of a shift, and the printing ink has to be removed from the ink fountains.